Add Model.is to compare models with each other

[MZanggl]

Proposed changes

Adds a little helper method to the Model instance to verify that two models are "the same".
Inspiration: https://laravel.com/docs/5.8/eloquent#comparing-models
Documentation PR: adonisjs/legacy-docs#382

Types of changes

What types of changes does your code introduce?

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

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• I have read the CONTRIBUTING doc
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works.
• I have added necessary documentation (if appropriate)

[coveralls]

Coverage increased (+0.002%) to 96.508% when pulling 5cd5aaa on MZanggl:feature/is into 6cd666d on adonisjs:develop.

[RomainLanz]

I like that, nice one!

Waiting for @thetutlage to review it.

[thetutlage]

May I know what use case it serves?

[MZanggl]

It's a convenience method, say for example in a user profile controller

class ProfileController {
  async show({ params, auth }) {
    const user = await User.firstOrFail(params.id)

    const canEdit = auth.user.is(user)
  }
}

[thetutlage]

Okay, that kind of makes sense. Would you mind creating a PR for branch v6.1.3?

The develop branch has code that targets the v5 of the framework

[MZanggl]

I changed the base branch.